1. Field of the Invention
The present invention relates to an ATM switching system, and in particular to an ATM switch system having an operation, administration, and maintenance function.
2. Description of Related Art
In data communication using the ATM (Asynchronous Transfer Mode) technique, a fixed length packet called cell is used as a transfer unit, which allows allocation of bandwidths required for communication channels for respective ones of destinations of multimedia information such as data, audio, and video. By inserting an operation, administration, and maintenance (OAM) cell on the communication channel, OAM processing such as fault notification and connection tests can be conducted on the communication channel. The OAM processing makes optimum data communication such as reconnection and alternate connection of communication channels possible depending on the situation of the data network.
As for such OAM processing, an OAM performance management function and an OAM fault management function in an ATM layer for processing a 53-byte cell are prescribed in Recommendation I.610 “B-ISDN OPERATION AND MAINTENANCE PRINCIPLES AND FUNCTIONS”, International Telecommunication Union (hereafter abbreviated to ITU-T).
According to the ITU-T recommendation I.610, the OAM processing functions include a fault management function, a performance management function, an activation/deactivation function, and a system management function. The respective processing functions are identified by codes of OAM types in a predetermined OAM cell format (see FIG. 20).
The fault management determines, when there occurs a failure, notifying other elements of the connection regarding the failure and providing the means to conduct a connection test. By providing the means to make reconnection or alternate connection on the basis of a result of processing conducted by the fault management function, reliability of data communication at the time of fault occurrence is improved. The performance management uses performance management cells inserted between user cells to measure an error rate, a loss of cell, and delay characteristics in the measured section. On the basis of a result of processing conducted by the performance management function, a network status can be periodically grasped to take best measures. The activation/deactivation function is used to detect a data communication activation condition and a data communication deactivation condition in the measured section.
Among them, the fault management function is prescribed as follows: “Alarm Indication Signal” (hereafter abbreviated to AIS) for forward fault notification, “Remote Defect Indication” (hereafter abbreviated to RDI) for backward fault notification, “Continuity Check” (hereafter abbreviated to CC) for periodic fault detection, and “Loop Back” (hereafter abbreviated to LB) for fault detection in a measured section.
Respective cells of the OAM fault management function operate in the ATM network as shown in FIGS. 23-25.
It is now assumed in the ATM network, as shown in FIG. 23, that a connection has been established between first and second ATM terminals 301 and 302 via first and second ATM switches 311 and 312 and first and second ATM transmission devices 321 and 322. If in such connection a fault has occurred on an ATM transmission line directed from the first ATM transmission device 321 to the second ATM transmission device 322, the fault is detected by the second ATM transmission device 322 located on the forward side, i.e., downstream side of the ATM transmission line. The second ATM transmission device 322 generates an AIS cell in order to give notice of the occurrence of the fault. And the second ATM transmission device 322 inserts the AIS cell thus generated between user cells, and sends them toward the second ATM switch 312. Upon arrival of the AIS cell thus sent out at the second ATM terminal 302 serving as an end point, an RDI cell is generated and sent out toward the first ATM terminal 301 located at the other end of the connection. By receiving the RDI cell, the first ATM terminal 301 can recognize the occurrence of the fault and the occurrence location. For example, the first ATM terminal 301 establishes a new path between the first ATM terminal 301 and the second ATM terminal 302 so as to avoid the faulty path.
The first ATM switch 311, as shown in FIG. 24, periodically generates a CC cell, inserts the CC cell between user cells, and send out them toward the second ATM switch 312. Upon finding that the CC cell has not been received in a predetermined time by using a timer installed within the second ATM switch 312, the second ATM switch 312 judges that an abnormality has occurred in the connection between the first ATM switch 311 and the second ATM switch 312. In the case where the second ATM switch 312 judges an abnormality to have occurred on the connection, the second ATM switch 312 typically sends out an RDI cell toward the first ATM switch 311 to give notice thereto to the effect. By receiving the RDI cell, the first ATM switch 311 can recognize the occurrence of the fault and the occurrence location. For example, the first ATM terminal 301 establishes a new path between the first ATM terminal 301 and the second ATM terminal 302 so as to avoid the faulty path.
If an administrator has conducted loopback establishment by defining the second ATM transmission device 322 as the LB location as shown in FIG. 25, then the first ATM transmission device 321 generates the LB cell and sends out the LB cell toward the second ATM transmission device 322. Upon receiving the LB cell, the second ATM transmission device 322 ascertains the LB location. When the LB location is itself, the second ATM transmission device 322 returns the LB cell toward the first ATM transmission device 321. Upon finding that the LB cell has not come back in a predetermined time by using a timer installed within the first ATM transmission device 321, the first ATM transmission device 321 judges that an abnormality has occurred in the connection between the first ATM switch 311 and the second ATM switch 312. For example, the first ATM terminal 301 establishes a new path between the first ATM terminal 301 and the second ATM terminal 302 so as to avoid the faulty path.
An ATM switch which conducts processing using such an OAM fault management function has been disclosed in, for example, Japanese Patent Application Unexamined Publication No. 10-262064 entitled “Terminating device for a plurality of lines and OAM processing method thereof”.
The conventional ATM switch includes an ATM switch core fabric having a line port section provided for each of ports thereof. The line port section includes a physical-layer terminating section and an ATM-layer terminating section. The physical-layer terminating section further includes an input physical-layer terminating section connected to incoming lines and an output physical-layer terminating section connected to outgoing lines.
As for an ATM cell inputted via one of the incoming lines, conversion from its format of the physical layer to an ATM cell having a line identifier for identifying the line through which the cell has arrived is first performed in the input physical-layer terminating section. A resultant ATM cell is inputted to the ATM-layer terminating section. In the ATM-layer terminating section, a synthetic identifier formed of the line identifier and VPI/VCI is converted to a connection identifier for internal processing having fewer bits. After usage parameter control (hereafter abbreviated to UPC) processing which performs adjustment of cell flow to set a number of flowing cells to a predetermined value, the ATM cells are subject to OAM processing in an OAM processing section.
The OAM processing section includes an internal processing connection management table for managing information required for each OAM processing in a unified way so as to correspond to each connection identifier for internal processing. By reading out corresponding connection management data for internal processing by referring to the connection identifier for internal processing of the arriving cell, corresponding OAM processing is activated and conduced. An ordinary cell, or an OAM cell which should not be subject to OAM processing at this switch because it is not specified as the end point of the OAM cell, is sent to the ATM switch core fabric.
On the other hand, a cell outputted from the ATM switch core fabric is subject to OAM processing in the OAM processing section in the same way for the purpose of transmission. Here, the generation and transfer of an OAM cell described with reference to FIGS. 20 to 22 are mainly conducted. Then, inverse conversion is performed from the connection identifier for internal connection to the synthetic identifier formed of the line identifier and VPI/VCI. In an output physical-layer terminating section, conversion to the signal format of the physical layer is conducted. A resultant cell is sent out to an outgoing line.
In such a conventional ATM switch, the synthetic identifier formed of the line identifier and VPI/VCI is converted to a connection identifier for internal processing. On the basis of the connection identifier for internal processing, connection management data to be subject to OAM processing is managed in a unified manner. Therefore, it becomes possible to conduct OAM processing for a plurality of lines every line efficiently.
In the above-described conventional ATM switch disclosed in the Japanese Patent Application Unexamined Publication 10-262064, however, it is necessary to provide the OAM cell receiving processing function on the line reception side and provide the OAM cell generation function on the line transmission side. In order to conduct the OAM processing on one bidirectional connection, therefore, it becomes necessary to perform setting and management on two ports by using software or the like. Thus there is a problem that the software processing becomes complicated.
In addition, other OAM processing functions in each line port as described above are implicated by an integrated circuit such as an application specific integrated circuit (hereafter abbreviated to ASIC) in many cases. In that case, it becomes necessary to pull in a large number of signal lines on the reception side and the transmission side. On the other hand, it is attempted to improve the processing speed by processing line data in parallel because of increased line speed at the ATM interface. Therefore, there is a cost problem in application of the ASIC which requires to pull in a large number of signal lines on the reception side and the transmission side.